Beer Fermentation and CO2

August 05, 2016

The next time you see a beer commercial or drink a cold draft, take the time to appreciate the importance of carbon dioxide in the brewing process.

Beer starts out as wort, a mix of water and natural grains. When Brewer’s yeast (a fungi) is added to the mix, it "eats" the starches and sugars in the wort while giving off alcohol and carbon dioxide (CO2) gas.

It is the infinitely variable combinations of water, grains, yeast, alcohol levels and the amount of carbonation which give each beer its unique color and taste.

During fermentation, the CO2 given off by the yeast was typically vented into the air. However, modern breweries now use CO2 capture systems. Once fermentation is complete, the brewing vats are sealed to build pressure and give the beer natural carbonation.To measure the CO2 levels before and during production, brewers use our 100% Sample Draw CO2 Meter. These meters are also used to spot check CO2 levels inside vats before workers go inside to clean them.

During bottling, CO2 gas is used to pre-fill each bottle before the beer is added. This process minimizes exposure to oxygen, reduces foam, and maintains the CO2 in the beer before it is capped. In commercial breweries, even the head-space (air below the cap in the bottle) is replaced with CO2 to keep out oxygen so that the bottled beer can last longer in non-refrigerated stores. In order to test CO2 during bottling, a high-speed sensor like our SprintIR Fast CO2 sensor is used, which can measure CO2 levels 20 times per second.

For most beer sold in kegs, CO2 from pressurized storage tanks is used to force the beer out of the tap. To protect customers and employees that work around pressurized CO2, breweries use our Remote CO2 Storage Safety Dual-Alarm. Because of the increasing use of high-pressure CO2 systems, it has become one of the most popular products we sell.

Interestingly, not every beer relies on CO2 for bubbles. The secret of Guinness Stout's creamy taste is its mix of nitrogen and carbon dioxide rather than pure CO2. The smaller nitrogen bubbles produce a smoother head. At taverns that serve Guinness on tap, they use a special nozzle that aerates the stout with nitrogen as it's poured. In cans of Guinness this is duplicated by inserting a capsule that releases pure nitrogen when the can is opened.